vec3 clover( float x, float y )
{
    float a = atan(x,y);
    float r = sqrt(x*x+y*y);
    float s = 0.5 + 0.5*sin(3.0*a + time);
    float g = sin(1.57+3.0*a+time);
    float d = 0.3 + 0.6*sqrt(s) + 0.15*g*g;
    float h = r/d;
    float f = 1.0-smoothstep( 0.95, 1.0, h );
    h *= 1.0-0.5*(1.0-h)*smoothstep(0.95+0.05*h,1.0,sin(3.0*a+time));
    return mix( vec3(1.0), vec3(0.4*h,0.2+0.3*h,0.0), f );
}
